body{
    margin: 0 auto;
}
.myFlex-x{/*在x轴方向上的上下左右都剧中*/
    display: flex;
    flex-direction: row;
    justify-content: center;
    align-items: center;
}
.myFlex-y{/*在y轴方向上的上下左右都剧中*/
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}